1. Field of the Invention
The present invention relates to a waste water classifying recovery apparatus for recovering waste water while classifying in a single wafer cleaning system in which wafers are cleaned especially one wafer at a time and particularly to a waste water classifying recovery apparatus in a wafer cleaning system in which rinse (cleaning with pure water) waste water after cleaning can be classified into cloudy rinse waste water and clean rinse waste water for recovery.
2. Description of the Prior Art
Generally, a wafer cleaning system of a multistage batch type or a single tank (bath or container) type has well been known and waste water classifying recovery means are different between both types.
The wafer cleaning system of a multistage batch type, for example as shown in FIG. 4, comprises: a chemical liquid A tank 30 (bath); rinse tanks (baths) 31, 32; a chemical liquid B tank 33; and rinse tanks 34, 35, wherein chemical liquid A and chemical liquid B are respectively supplied to the chemical liquid A tank 30 and the chemical liquid B tank 33 through a chemical liquid A supply line 37 and a chemical liquid B supply line 38, while rinse water (pure water or ultrapure water) is supplied to all the tanks through a rinse water supply line 39. A transport robot moves a carrier in which many wafers are included sequentially through the chemical liquid A tank 30; the rinse tanks 31, 32; the chemical liquid B tank 33, the rinse tanks 34, 35 and the like so that the wafers are sequentially immersed into the tanks batchwise.
In a cleaning system of this type, waste water (including waste liquid, hereinafter same as this) can be recovered from each tank while classifying. That is, the chemical liquid A waste water is recovered from the chemical liquid A tank 30, the chemical liquid B waste water is recovered from the chemical liquid B tank 33, first rinse (cloudy rinse) waste water from the rinse tanks 31, 34 and second rinse (clean rinse) waste water from the rinse tanks 32, 35.
A wafer cleaning system of a single tank batch type, as shown in FIG. 5, has been proposed (see "VLSI Process System Handbook," published by Kohgyo Chosakai Co., Tokyo), in which chemical liquid A 43, chemical liquid B 44 and rinse water 45 are selectively supplied to a cleaning tank (container or vessel) 48 through a mixing chamber 46, wafers are placed in a cassette 41 in plural number and the cassette 41 are revolved in the cleaning tank 48 by a rotary shaft 47, so that the wafers are cleaned in a immersion treatment.
In a wafer cleaning system of this type, a waste water (drain) line 42 is provided with a three way valve 40 and the like, and the three way valve 40 is operated for draining in each of timings of change of cleaning by the chemical liquids A, B and the rinse water, so that chemical liquid A waste water, chemical liquid B waste water and rinse waste water are classified and recovered.
On the other hand, as shown in FIG. 6, a single wafer cleaning system of a single tank (container or vessel) type has been known, in which wafers 2 are placed in a treatment tank 1 one wafer at a time and the wafers sequentially receive spray of the chemical liquids A, B and the rinse water. In a wafer cleaning system of this single tank type, since the wafers are sequentially sprayed with the chemical liquids and the rinse water one wafer at a time, classifying recovery of waste water is hard to be effected with a single waste water line 50 and mixed waste water of chemical liquids and rinse water has conventionally been collected.
The wafer cleaning system of a multistage batch type is advantageous in waste water processing, since each waste water in chemical liquid and rinse systems can be recovered while being classified, whereas there has been a tendency that as a wafer diameter is increased, a wafer cleaning system of a single tank type becomes adopted, since an installation space for tanks is increased.
As shown in FIG. 5, a wafer cleaning system of a single tank type is harder for classifying recovery than a wafer cleaning system of a multistage batch type because all the waste waters are recovered through the single waste pipe (drain) line 42, but since a wafer cleaning system of a single tank type in which a cassette is immersed in a treatment tank is allowed to have a comparatively long time in cleaning, classifying recovery can be effected by operating a three way valve 40 in synchronization with each step of cleaning.
However, in a single wafer cleaning system of a single tank type, as shown in FIG. 6, in which wafers are sequentially sprayed with chemical liquid and rinse water one wafer at a time, since each cleaning time for a wafer is short (on the order of 1 to 3 minutes) and therefore, timing in waste water recovery is hard to be correctly matched, there has been much of difficulty in classifying recovery of waste water from the single common waste water line 50. Therefore, there has conventionally been no way but to recover mixed waste water of chemical liquid and rinse water: classifying recovery of waste water into chemical liquid and rinse water, and further classifying recovery of the rinse water into cloudy rinse waste water and clean rinse waste water have been very hard. Especially, when classifying recovery of waste water into cloudy rinse waste water and clean rinse waste water is impossible, a trouble arises in purification and recycling of waste water and there has remained a problem that reasonable water utilization cannot be achieved.